Pulsation dampener



Dec. zo, 1935 M LUDWIG 2,727,470

PULSATION DAMPENER Filed April l, 1952 2 Sheets-Sheet l Dec. 20, 1955 M. LU DW l G PULSATION DAMPENER Filed April l, 1952 2 Sheets-Sheet 2 irma/vif United States Patent O PULsATloN DAMPENER Milton Ludwig, Berkeley, Calif., assi'guor, by mesne assignments, to California Research Corporation, San Francisco, Calif., a corporation of Delaware Application April 1, 1952, Serial No. 279,887

17 Claims. (Cl. 10S-223) This invention relates topulsation dampeners. More particularly it relates to means for filtering strong, high frequency pressure pulses from liquid ow in a pipe.

There exists a trend in pump design for high pressure pumping stations, such as stations intended to pump crude petroleum and rened petroleum products, to provide multiple piston pumps, having a small piston displacement but operating at high speed. As a typical example, for the purpose of pumping 26,000 barrels per day (B. P. D.) of diesel oil into an eight inch line, a pump may be employed having ten single acting cylinders operating at a crankshaft speed of 360l revolutions per minute (R. P. M.). Such a pump will, of course, impart a pulsating flow to the liquid flowing in the suction line and in the dischargel line of the pump'. Each pulse consists of a wave of pressure having a peak and valley or low value. The pulsation is complex and can be best understood by comparison with a simpler pump.

Assume, therefore, that liquid is being pumped into or from a line by a pump consisting of one double acting cylinder operating at 60 R. P. M. Pulsation, or pressure surges will be produced in the line at a fundamental frequency equal to twice the pump speed, i. e., two cycles per second (C. P. S.). ln a typical liquid such as petroleum or diesel fuel, the speed of the pressure wave will be about 3600 ft./sec., hence the wave length for the fundamental frequency component will be about S600/2 or i800 feet.

Referring to Figure l of the drawings, iiow of the liquid in a line connected to a one cylinder, double acting, 60 R. P. M. pump is plotted against time. The form of the resulting curve approximates that of a repeating half sine wave. Because of the effect of finite connecting rod length and other factors, the waves or pulses are not, however, perfect half sine waves.

Referring to Figure 2 of the drawings, the wave form of ow of liquid in a line connected to a double acting iive cylinder 360 R. P. M. reciprocating pump is similarly illustrated. In connection with Figure 2, a crank angle spacing of 72 is assumed for the pump. Each stroke of each piston creates a pulse, and in Figure 2, the successive overlapping pulses created by the tive double-acting pistons are represented by the approximately half sine waves at the bottom. The pulses corresponding to the five forward strokes of each cycle are represented by the solid line curves numbered, 1, 2, 3, 4 and 5 and the pulses corresponding. to the tive return strokes of each cycle are represented by the broken line curves numbered 1', 2', 3', 4' and/5.v

Above the curves 1, 2, etc; and 1', 2', etc. is a curve D of complex wave form-and a median line M. The amplitude of the curve D is not drawn to scale and may be exaggerated with respect to an actual installation, such exaggeration being employed for clarity. The curve D represents the wave form ofthe flow of liquid caused by a'double acting, five cylinder 360 R. P. M. reciprocating pump, and it is the resultant of the curves,

2,727,470 Patented Dec. 20, 1955 2 1, 2, etc., and 1', 2', etc. The median line M represents the mean flow and the cross hatched areas above and belowthe line-.M represent the excess and deficiency of actual flow with respect to the mean flow represented by`Mz. The'curve D', median line M andthe cross hatched areas of: Figure 1 have similar meanings.

A comparison of Figures l and 2 reveals certainthings of significance in connectionl with the presentI invention, among them being the following: The one cylinder, double acting 60 R. P: M. pump whose ow patternV is represented by Figure l gives rise to a low frequency (2 C..P". S.), long wave length. (calculated as 1800 ft.) flow pattern in which therefis a large variation of-actual ow above and below mean flow. The five cylinder, double acting 360 R. P. M. pump whose flow pattern is represented' by Figure 2 gives rise to a high frequency (60 C. P. S.), shortwave length (calculated as 60.ft.) flowpatternin which there is asmall variation of actual flow above and below mean flow.

Inspection of Figure 2 will also reveal that the ow pulsates at a dominant frequency of l0 cycles per revolution of the crankshaft andI that, at a crankshaft speed of 36) R. P; M., the dominant frequency of the pulsating flow will be 6X 10:6() C. P. S. There will, of course, be harmonics-of this dominant frequency and thereV may be: sub-harmonic frequencies and also other frequencies caused by the effect of finite connecting rod. length, valve leakage. and other factors. The curves D and D are idealized. curves representing theoretical ow patterns. Ine practice, the flow pattern is more complex. However, a given system operating under a given set of conditions willV exhibit a ow pattern having a dominant frequency, and in the case of a high speed, multiple piston pump. this dominant frequency will be a high frequency associatedy with a correspondingly short wave length.

A11l important advantage of a high speed, multiple pistonk pump is made evident by comparison of Figures, 1 and. 2; the pulsations of a one cylinder, double acting 60 R. P.. M. pump have a very large amplitude, hence flow rate varies from zero to as much as, say, 60%. above mean iiow rate, whereas the pulsations of a ve cylinder, double acting360 R. P. M. pump have a very small amplitude with the result that the liow rate is relatively smooth; it does not, in a typical case, exceed the mean flow rate by more than about 1.4% nor fall more than about 5.5% below the mean flow rate.

In practice, however, high speed pumps such as the exemplary double acting, five cylinder 36,0 R. P. M. pump discussed above, whose ow pattern is illustrated in Figure 2, give rise to serious difficulties. These difficulties are sensibly indicated by extreme vibration of pipe bends, relatively short lengths of connecting pipe or branch pipe and other mechanical phenomena which are actually or potentially destructive. Analysis reveals that these diiculties are due to the peculiar effects of the high fundamental or dominant frequency of such a pump and/or to strong harmonics or sub-harmonics of such frequency.

It is an object of the present invention to provide a means for relieving the severe vibrations and other similar mechanical diiculties which have been experienced in connection with high speed reciprocating pumpsl and other pumps which give rise to a pulsating iiow having a high fundamental or dominant frequency.

It is a further object of the present invention to provide a filter means which is uniquely adapted to lter out or dampen high frequencies which exist in the ow pattern of high speed multiple cylinder pumps and the like and which are likely to cause excessive vibration in pipes.

To illustrate the type of pulsating ow and its characteristics with which this invention is concerned, to illustrate the filter means employed in accordance with this =wave of curve D.

Y tuations.

invention and to illustrate the results obtained thereby, reference will be made to the accompanying drawings in which Figure l, as mentioned above, is a graphic representation of the iiow pattern of a low speed, one cylinder double acting pump.

Figure 2, as mentioned above, is a graphic representation of the flow pattern of a high speed, five cylinder double acting pump.

Figure 3 is a graphic representation of the ow patterns of both a low speed pump and a high speed pump, the curves of said figure being fragments of the curves of D'and D of Figures l and 2.

Figure 4 is a diagramatic view of a system including a high speed pump and a surge chamber and choke tube in accordance with the preferred embodiment of the invention.

Figure 5 is a diagramatic view of a system similar to that of Figure 4, but without a choke tube.

Figure 6 is a diagramatic view of a system similar to that of Figure 5, but with the surge chamber installed 'as a branch rather than in the path of ow of liquid.

Figure 7 is a diagrammatic view of a system similar to that of Figure 6 in which, however, the capacitance medium in the surge chamber is separated from the liquid owing in the line.

Figure 8 is a diagrammatic view of a system similar to that of Figure 4 in which, however, a second surge chamber is provided.

Referring now to Figure 3, fragments of the curves D and D of Figures l and 2 are plotted on the same set of coordinates. As indicated each of the pulses or waves of the curve D has a length of 60 feet. The curve D' shows only a fragment (one-fifth) of a wave. Superimposed upon each of the curves D and D' is a pipe bend 10 spanning a distance of thirty feet and a thirty foot pipe length 11. It will be apparent that the pipe bend 10 is subjected, under the conditions illustrated, to a relatively large pressure diferential, AP, between the trough and thecrest of a wave of curve D and that it is subjected lto only a very small pressure dierential, AP', by the It will be apparent that the body ofy uid in pipe length 11 has a length corresponding to Yonel half of a wave length of curve D whereas the fluid in a similar pipe length, having a similar length (30 feet) kcorresponds to only a very small fraction of a wave length of curve D.

Under these conditions certain results can be expected and are, in fact, experienced. The relatively large pressure differential AP on the pipe bend 10, willof course,

oscillate, and opposite ends of the pipe bend may be subjected to relatively large, and opposite pressure uc- If these fluctuations should occur at or near the mechanical frequency of the pipe bend, the latter may resonate and the resulting severe mechanical vibrations may damage or destroy the pipe bend or its fittings. The thirty foot pipe 11 will contain a body of uid which is also thirty feet in length and which may resonate at the 60 C. P. S. fundamental frequency of the pulsating ow. Again, severe vibrations may result with consequent damage.

Neither of these conditions is likely to occur in the case of the same pipe bend and the same pipe length when subjected to the low frequency pulsating flow represented by the curve D'.

In dampening pulsations in the pulsating flow of liquids it has been proposed heretofore to use an easily compressible uid, i. e., a gas, to absorb pressure peaks and to supply pressure during pressure lows. A typical dampener or acoustical capacitance of this character employs a bulb or other suitable vessel provided with a diaphragm which separates the vessel into two portions. One portion, on one side of the diaphragm, is filled with a. gas and a suitable inlet, inlet valve and pressure gage may he employed to admit gas, to register its pressure, and to manipulate the gas pressure from Vtime to time to correct'.

pressure transmitted through this connection to the dia-- phragm compresses the gas, and during pressure lows the compressed gas expels liquid under higher pressure into the main stream of liquid. lThe gas chamber therefore behaves as an acoustical capacitance or surge chamber and serves, in some measure, to dampen pulsations in the line.

A gas chamber capacitance or gas filled surge chamber of this character has particular application to a low frequency, large amplitude pulsating liquid ow. The high compressibility of the gas adapts it to absorbing the relatively large excess volume of liquid (corresponding to the cross hatched areas above the median line M of Figure l) during pressure peaks and to restore this excess during pressure lows.

However, a gas filled surge chamber has certain disadvantages, among which may be mentioned the following. In a gas filled surge chamber having a diaphragm or some other expansible mechanical member which constantly exes during use, such member is subject to wear and requires replacement fromtime to time. Also gas leakage .is likely to occur, especially in connection with high pressure pumps. Another type of gas filled surge chamber employs a gas in direct contact with the liquid which is-being pumped. In this type of surge chamber the gas dissolves in the liquid.

One of the objects of the present invention is to provide a surge chamber or acoustical capacitance for a liquid transmission system involving pulsating ow, especially liquid ow which pulsates at a high fundamental frequency, which obviates the necessity of using an easily compressible uid as the capacitance or pressure absorption medium.

bAnother object of the present invention is to provide a liquid filled surge chamber for absorbing and dampening high frequency pulses in a liquid transmission system.

Yet another object is to provide a filter including a liquid filled surge chamber for filtering high frequencies, wherein the liquid which is being pumped and whose pulsations are being filtered, itself constitutes the capacitance medium.

A further object of the invention is to provide a filter for strong high frequencies in a liquid transmission system, which includes a liquid filled surge chamber of convenient size but adequate to absorb excess flow during pressure peaks, and which also includes an inductance or choke tube cooperable with the surge chamber to dampen selected high frequency pulsations.

These and other objects of the invention will be apparent from the ensuing description and the appended claims.

In accordance with the present invention, I provide, in conjunction with a reciprocating pump or other source of pulsating pressure, and more particularly in conjunction with a source of pulsating pressure which gives rise to a dominant high frequency, a capacitance or surge chamber which is filled with a compressible medium whose compressibility is small compared to that of a gas, and I also provide an acoustical inductance, preferably in the form of a choke tube, to further dampen such high frequency pulsation;

In general terms, the volume, V, of such surge chamber, i. e., the volume of the compressible medium, is selected in the light of its compressibility or the related property of bulk modulus k, and in the light of the excess volume of liquid q, corresponding to the peak pressure at the fundamental frequency f. Referring to Figure 2, the excess volume q is represented by the cross hatched area above the median line M and bounded by that line and any one of the waves of curve D. Inasmuch as this volume q, or a volume approximating q, is to be absorbed by the volume of liquid in'the surge chamber, it follows that the volume V Yand the compressibilityoftleicapacitance medium'must be such that, atthe peak vpressure P, said medium will compress sufficiently to accomplish this result.

As pointed out hereinabove, Vsurge chambers heretofore used have been of the gas filled type, Vwherein the capacitance medium ishighlycompre's'sible. For certain types of flow, such as that represented by Figure 1, a highly compressible medium is desirable because an unwieldy volume of a slightly compressible medium would be required. The feasibility of aunediurn of low compressibility for dampening high frequency pulsations can be illustrated by the following calculations:

Assume a doubleacting five cylinder pump operating at a speed of 360 R. P. M., hence creating a fundamental frequency of 60 C. P. S. Assumefurtherthat diesel fuel is being pumped into an eight inch line at the rate of 26,000 B. P. D., or 1.68 cu. ft. per second. lt is safe to assume that the excess flow at peak pressure averages about 1% for a period of l/ l0 of a revolution of the crankshaft, or for a period of'only 1/ 60 of a second. The excess flow rate is equal to 0.01 Yl.68=0.0l68 cubic foot per second. This excess flow rate occurs during only l/ 60 of a second during each pulse at the fundamental frequency. Consequently the excess volume q, is equal t0 0.0168 X610=0.0028 eu. ft.

or'0.48 cu. inch. Assuming a surge chamber volume of 16 cubic feet or 27,600 cu. inches, filled with dieselfuel having a bulk modulus of 150,000 p. s. i., the increase of pressure required to compress 0.48 cu. inch of diesel `fu'el into a 16 cu. ft. surge chamber already filled with diesel fuel, is given Vby the equation AV 0.48 AP: 100,000xisdoooxZGOO-ae p. s. 1.

lt will, therefore, be apparent that a very moderate pressure dierential (2.6 p. s. i.) and a liquid filled surge chamber of moderate volume (16 cu. ft.) will function as a capacitance to absorb peak flow.

Referring to Figure 4, in which the preferred embodiment of my invention is illustrated in diagrammatic form, a high speed pump is shown at which is driven by a motor 16 through a driving connection 17. The pump 15 takes liquid through an inlet 18 and discharges through a short length of pipe 19 into a surge chamber -20 which is intended to discharge into a vline 21. Interposed between the surge chamber 20 and the vline 21 is a choke tube 22 of restricted cross section compared to that of the line 21. The surge chamber 20 is completely filled with the liquid which is being pumped, it isvlocated in close proximity to the pump 15 and its volume V is sufficient in relation to flow rate Q bulk modulus k, excess peak volume q, etc. that it will absorb all or a large proportion of the excess volume q during pressure peaks and will thereby moderate the flow and dampen the fundamental frequency.

In designing a choke tube, several considerations are involved. The function of the surge chamber or capacitance 20 is to store excess fiow during pressure surges while the function of the choke tube or inductance 32'is to resist influx of liquid from the surge chamber during pressure peaks, and to allow relatively free fiow during pressure lows, meanwhile allowing constant, but dampened flow of liquid into Athe line. The inductance L of a short choke tube is given by the equation L--gB wherein the symbols L, p, etc. have the meaning given in Table I below. Since p is a constant for a given liquid and g is a universal constant, it is apparent Athat the inductance L, is directly proportional to the length y of the choke tube and is inversely proportional to the crosssectional area B of the choke tube. The :greater the inductance, the more effective the choke tube for the purpose. However, other considerations limit both 'its length y and its cross-sectional area B. Thus, if a pump creates a 60 C. P. S. fundamental having, as a harmonic, a strong C. P. S. frequency, the liquid in a thirty foot straight length of choke tube would resonate vat the 60 C. P. S. fundamental frequency and the liquid in a fifteen foot straight length would resonate at the 120 C. P. S. harmonic. Either condition is objectionable because of its possible destructive effect on the choke tube. Moreover it can be shown by mathematical analysis that the filtering effectiveness of a long choke tube may be less than that of a shorter choke tube. Hence a shorter length, e. g., eight feet would be chosen. In general, "the choke tube length is selected to be a small fraction of 'the wave length of any strong frequency.

The diameter or cross-sectional area of the choke tube is limited by reason of pressure drop caused by the 'constriction. Factors which require consideration are pump pressures and volume of flow. Thus, in a typical instance, where a five cylinder double acting 360 R. P. M. lpump is discharging 26,000 B. P. D. of petroleum into an eight inch line, it can be shown that a pressure loss of about 2 p. s. i. can be expected in a choke tube of four inch diameter and an eight foot length. A three inch or a two inch diameter choke tube of the same length would cause a pressure drop, under these conditons, of about 7 p. s. i. or 50 p. s. i., respectively. Hence a four inch diameter, eight foot length of choke tube would be preferred provided that, by calculation, by reference to a table, or by trial and error it is determined that the objectionable high frequencies will be effectively filtered out.

Referring now to Figure 5, in which similar parts are similarly numbered, a system is there shown which is the same as that of Figure 4 except that no choke tube is employed. The surge chamber 20 has a volume V which is determined as 'm the case of the surge chamber of Figure 4. This system is not as effective as that of Figure 4 which employs a choke tube in conjunction with a surge chamber, but it will dampen strong high frequency pulsations to a considerable degree.

Referring now to Figure 6, in which similar parts are similarly numbered, a surge chamber 20a is rprovided which, like the surge chamber 20 of Figures 4 and 5, is filled with the liquid which is being pumped. However, the chamber 20a, instead of being incorporated in the path of flow of the liquid, is employed as a branch chamber and is connected to the line 21 by means of an open connecting tube 23.

Referring to Figure 7, in which similar parts are similarly numbered, the branch surge chamber 20a is provided with a flexible diaphragm 30 at its junction with the connecting tube 22, such diaphragm being impermeable to liquid. A liquid capacitance medium 31 fills the chamber 20a. This liquid medium may be the same as the liquid which is being pumped through the line 21 or it may be a different fiuid, e. g., a fluid having a greater compressibility, hence requiring a lesser volume V.

It will be apparent that in each of the embodiments of the invention illustrated in Figures 5, 6 and 7, the liquid filled surge chamber 20 or 20a or, more accurately, the liquid therein will act as an acoustical capacitance to absorb excess flow at peak pressures and to release liquid during pressure lows, thereby moderating pressure pulsations in the line 21. This moderating or filtering eect will be exerted in the line 21 beyond the surge chamber and it will also be exerted in the pipe between the surge chamber and the pump. Also, if a surge chamber is similarly installed in Athe intake line 18, it will similarly moderate pulsations therein.

A liquid filled surge chamber such as shown at 20 and 20a in Figures 5, 6 and 7 has a substantial range of usefulness in moderating high frequency pulsation in liquid transmission systems. However, it is more generally oil into an 8 inch line.

effective, and is more effective in ltering selected high frequency pulsations, if, as in Figure 4, it is coupled with an inductance, such as a choke tube, and if the capacitance, C, and the inductance, L, of the surge cham ber and choketube are properly related to other conditions prevailing in the system.

The systems shown in Figures 6 and 7 may be modified to embody a choke tube between the surge chamber and the line.

In connection with the conjoint use of a choke tube and a surge chamber such as illustrated in Figure 4, it is well to point out that this design is preferred because of the additional dampening effect of a choke tube and because such a choke tube can be designed to meet the requirements of a particular pumping system. An additional mechanical advantage results. Thus it frequently happens that a high speed pump vibrates severely and the mechanical vibration is transmitted to the line. The interposition of a choke tube of small diameter provides a mechanical, as well as an acoustical, dampener which dampens mechanical vibrations and lessens vibration of the line.

However, it should be noted that other systems such as shown in Figures 5, 6 and 7 may act as two element lters for pulsating flow. Thus, the line 21 of Figure 4 may itself have resistance characteristics such as to function as one element of a capacitance-resistance filter. In the case of a long pipe line, this resistance may sutice to meet the requirements of a matched capacitance and resistance for effectively filtering out the fundamental or dominant frequency. Also, the connecting pipe 23 of lFigures 6 and 7 may be so designed as to function as inductance to match the capacitance in such way as to absorb or dampen selected high frequencies.

Referring now to Figure 8, a system similar to that vof Figure 4 is illustrated but with the addition of a second surge chamber 20h. A second surge chamber such as that shown at 20b may be desirable where, for example, the pump pumps into a short line whose input impedance cannot be calculated with as great a certainty as the' input impedance of a long pipe line.

As a specific example of the practical application of the principles of my invention the following conditions may be assumed: A double acting ve cylinder 360 R. P. M. pump is discharging 26,000 B. P. D. of diesel The dominant frequency of the pulsating tlow will be ten times the revolutions per minute, or 60 C. P. S. A surge chamber of 16 cubic feet volume is adequate to absorb excess ow at peak pressures. As explained above, an eight foot length of choke tube will not resonate at the dominant 60 C. P. S. frequency nor at a harmonic frequency of l2() C. P. S. An eight foot choke tube of four inch diameter will result in a pressure loss not exceeding about 2 p. s. i. provided long tapers are used at the ends of the tube.

As a guide in estimating the effectiveness of this 16 cu. ft. surge chamber and 8 ft. length, 4 inch diameter choke tube in filtering strong high frequencies, the following calculations may be made, employing the following notation:

Table I 1 -:velocity of pressure surge, F. P. S. d=pipe diameter, feet f=frequency of pulsation, F. P. S. g=gravity constant=32-2 h=pipe wall thickness, feet j=complex operator=\/'l k=bulk modulus for liquid, P. S. F. ker-effective bulk modulus, P. S. F. t=time, seconds Y y- -length of choke tube, feet v=Poissons ratio p--uid density, lb. mass per cu. ft. w= 21rf l A=crosssectional area of pipe, sq. ft.

B=cross=sectiona1 area of choke tube, sq. ft.

C=capacitance of surge chamber, ft.5 per lb.

L=inductance of choke tube, lb. sec.2 per ft.5

R=dynamic resistance of pipe line, lb. sec. per ft.5

V=volume of surge chamber, cu. ft.

P=pressure, P. F. S.

Po,=pulsating pressure without surge chamber and choke tube Pp=pulsating pressure at pump with surge chamber and choke tube inn-:pulsating pressure at line with surge chamber and choke tube Q=ow rate, C'. F. S.

E=voltage in equivalent electrical circuit I :currentin equivalent electrical circuit The capacitance of a surface chamber can be calculated by analogy with the formula for the capacitance of an electrical condenser:

v l E L- The equivalent relation for a choke tube is 5 nl n Hence, the inductance of a choke tube is given by the formula (This assumes that frictional losses are negligible and that the liquid content of the choke tube accelerates simuld taneously. For a tube which is a small fraction of a wave length, e. g., 1/fs, the latter assumption is valid, and for a short tube length the pressure loss is quite small.) Other variables for which formulae should be derived are the surge impedance or dynamic resistance, R, of the pipeline intol which the liquid is being pumped, and the wave velocity, a. The familiar water hammer equation for the pressure developed by a ow change Q is gAQ from which, by analogy to the equation (8) E -RI it follows that the surge impedance is given by the formula The wave velocity is given by the equation tube combination maybe indicated by the ratios PL/Po and PP/Po, where Po is the pulsating pressure without 9 the filter; P1. is the pulsating pressure with the lter, in the line into which the lter discharges; and PP is the pulsating pressure, with the Jlter, at the discharge of the pump. It will be understood, of course, that there will be a set of values of Pr., Po and Pp for each such frequency.

These pressure relations are related to certain characteristics of the system as follows:

P l-PLC-l-jmRC 1n= 1= P0 l-wZLC-i-jwRC' The scalar values (magnitudes) of these vectors can be expressed as follows:

P0 \/(32L01)2+ @RC 2 ce nf: Mary n.)

P0 R P0 in Table ll below, values of PL/Po and PP/Po are given for various values of wRC and wZLC.

Table Il Pr. PP wRC wLC P-O Po 1 .500 .560 i .277 .020 2 8 138 .566 16 .0660 .532 32 0322 .512 1 250 .253 4 200 .233 4 i s .124 .277 16 0664 .265 32 .0320 .25s 1 .125 .126 4 .117 .131 s 8 .094 .133 i 16 .058s .131 32 .0312 .129

Reverting to the specific conditions assumed above, the numerical values of the terms needed to apply to Table I are as follows:

A=0.347 sq. ft. (pipe cross sect.) B=0.0885 sq. ft. (choke tube cross sect.) y=8 ft. (choke tube length) V=l6 cu. ft. (surge chamber volume) ke=l50,000 p. s. i. (eifective bulk modulus) p=501bs./cu. ft. (density of petroleum) Prom these data, it follows that L @Le 14.7 rizzo-mem it will be seen that the pulsating pressure P1. in the line is reduced by the 16 cu. ft. surge chamber- 8 ft. long, 4 inch diameter choke tube filter, to 6.9% of its value without the lter, and that the pulsating pressure Po at the pump is reduced to 22.9% of its value without the filter.

Similar calculations reveal that the corresponding values of PL/Po and PP/Po at lower frequencies will be somewhat greater. Such frequencies may be caused by operating the pump at a lower speed or by the effect of finite length of the connecting rod. For example, at a requency of 30 C. P. S. the values are 0.28 and 0.52, respectively. Nevertheless, the pulsating pressure is substantially reduced even at the lower frequency. Morcover, the lower frequencies are not as harmful. Subharmonics are not, in any event, amplified. Also, redesign of the filter, e. g., to employ a choke tube of smaller diameter, will result in more effective ltering of lower frequencies. Higher frequencies, e. g., a 120 C. P. S. harmonic, will be even more eifectively reduced than the C. P. S. frequency.

Table I reveals certain general relationships which are of value in designing a filter. Thus, high values of wRC reduce the pulsating pressure both in the line and at the pump and high values of w2LC reduce the pulsating pressure in the line without materially affecting the pulsating pressure at the pump.

It will, therefore, be apparent that a novel type of filtering system for filtering high frequency pulsations in pulsating liquid iiow has been designed. This system employs a liquid capacitance medium or other capacitance medium of low compressibility compared to a gas. Such a capacitance or surge medium is especially adapted to use with high frequency pulsating flow, and its effectiveness is greatly improved by using it in conjunction with a choke tube or inductance. The disadvantages of a gas filled surge chamber are avoided and in its preferred form my system employs the liquid whose flow is being regulated as the capacitance medium, thereby simplifying design, operation and maintenance.

l claim:

l. in combination with a liquid transmission system comprising a source of pulsating pressure giving rise to periods of peak flow which occur at a high frequency and which are characterized by a small excess flow of liquid over mean flow, a surge chamber filled with a compressible medium whose compressibility is small conpared to that of a gas but whose volume and compressibility are such that excess peak pressures sutiice to compress said medium by an amount which is substantial in relation to the volume of said excess flow, and means connecting said surge chamber with said system whereby said medium is alternately compressed and expanded in respouse to pressure peaks and presure lows of said pulsat- O ing pressure, respectively, and whereby the pulsating ow of liquid in said system is dampened.

2. ln combination with a liquid transmission system comprising a source of pulsating pressure giving rise to periods of peak flow which occur at a high frequency and which are characterized by a small excess ow of liquid over mean flow, a surge chamber filled with a liquid medium and means connecting said surge chamber with said system whereby said medium is alternately compressed and expanded in response to pressure peaks and pressure lows of said pulsating pressure, respectively, and whereby the pulsating flow of liquid in said system is dampened.

3. In combination with a liquid transmission system comprising a source of pulsating pressure giving rise to high frequency flow having alternating periods of peak flow and low flow associated with pressure peaks and pressure lows, respectively, and wherein the excess flow associated with pressure: peaks -is small compared to the mean ow, a surge chamber so connected with said system as to be maintained full ofthe liquid which is being transmitted, said surge chamber having a suicient'volume in relation to compressibility of said liquid and to the flow of liquid in-excess yof Vmean flow andthe pressure thereof in rexcessofv mean pressure during periods ofV peak ow that'said excess pressure will compress at least a substantial proportion of saidexcess ilow in said volume during periods of peak iiow.

4.1 The combination of claim 3 wherein said surge chamber is located so as to be in the path of flow of liquid insaid system.

5 j The combination of claim 4 including a choke tube of restricted cross section also located so as to be in the Ph' 0f flow of liquid in said system and being located so as to regulate efliux ofV pressure surges from said surge chamber.

6. The combination of claim 3, wherein said surge chamber is so connected to said system as to constitute abranch thereof andto absorb peak flow therefrom and to restoreow thereto during pressure peaks and pressure lows, respectively.

7. The combination of claim 6, wherein said branch surge chamber is so connected to said system as to allow passage of liquid from the system into the surge chamber to'provide the capacitance medium.

8: The combination of claim 6, wherein said branch surgefchamber is provided with a separate body of liquid to serve as the capacitance medium, and wherein said capacitance medium is provided Withan impermeable pressure transmitting connection between the liquid owing inthe system and the capacitance medium Wherebysaid medium is alternately compressed and expanded inresponse toV pressure peaks and pressure lows of said flow.

9; Avliquidtransmission system comprising a source of pulsatingl flow having a dominant high frequency giving rise to peaks'of excess pressure over mean pressure and to peaks of excess ow over mean ow,a pipe for transmitting-lsaid pulsating 110W and a filter for dampening said fundamental frequency, saidv filter comprising a surge chamber filledA with a liquid medium and so connected with said system as to be compressed by pressure peaks and expanded by pressure lows in the system, said chamber having a volume which is suiiicient in relation to the compressibility of the liquid medium and to said excess pressure and-said excess kflow that said medium will contact and expand in response to said pressure peaks and pressure lows by a volume AV which suces to substantially dampen said fundamental frequency.

10. A liquid transmission system comprising a source of pulsating flow having a dominant high frequency giving rise to peaks of excess pressure over mean pressure and to peaks of excess ow over mean ow, a pipe for transmitting said pulsating ow and a filter for dampening said fundamental frequency, said iilter comprising a surge chamber lled with a liquid medium and so connected with said system as to be compressed by pressure peaks and expanded by pressure lows in the system, vsaid chamberl having a volume'which is suicient in relation to the compressibility of the liquid medium and to said excess pressure and said excess flow that said medium willv contract and expand in response to said pressure peaks and pressure lows by a volume AV which suffices to substantially dampensaid fundamental frequency, said filter also comprising a choke tube to moderate pulses from saidsurge chamber.

1l. In a liquid transmission system including a source of high: frequency pulsating pressure giving risel to a dominant frequency, the improvement which comprises a'vlter for dampening pulsations of said frequency fr saidlter comprisinsga liquidlled surge chamber havingE a` volume V of compressibleliquid medium;

12 means providing a pressure connection between liquid flowing in the' systemiafnd said liquid medium to cause compression-and expansion thereof in response to pressurey pulses inthesystem, and an acoustical inductance i of inductancev L associated withsaid surge chamber to improve the effectiveness of the latter in dampening pulsations of frequency f, the values of V and L being such as to maintain the ratio PL/Po substantially less than unity, Pr. being the pulsating pressure of the system with said filter andPo being the pulsating pressure of the system without a filter.

12. A filter for a liquid transmission system having a pulsating flow of fundamental frequency f and a dynamic resistance R, said'iilter' comprising'a surge chamber of volume V, a choke tube of Vcross sectional area B, length y and acoustical iuductance L and means so connecting said surge chamber and choke tube with said system that pressure pulsations in the system will alternately compress and expand a compressible medium in the surge chamber to dampen saidpulsating flow and pulsations in the system caused by compression and expansion of said medium will be dampened by said choke tube; the said quantities V, B and y being selected in relation to the acoustical capacitance C of a medium having a small compressibilitycompared yto a gas, and in relation to said frequency f anddynamic resistance R, that the function l #my is substantially less' than unity.

13. The filter of claim l2, wherein said quantities V and B andi-y are selectedvso that/the function 2 `/1 +621?) f n1 t/zfWLC- 1 2+ 21ff Rm2 is also substantially less than unity.

14. In combination with a high speed pulsating pump giving rise to high frequency pulsating ow having a fundamental frequency f ofthe order of l0 to 100 cycles per second, and a transmission system for transmitting pulsating liquid ow from said pump, said system having a dynamic resistance R, a lter for dampening pulsations of frequency f and harmonics thereof, said filter comprising a surge chamber filled with a liquid medium of acousticalcapacitance C and volume V, means connecting said liquid medium with said system to alternately compress and expand said medium in response to pressure pulsations in the system, and a choke tube of acoustical inductance L associated with said surge chamber to further dampen pulsations of frequency f, said volume V and inductance L being selected so that each of the functionsand zffL 2 1 1 N/ Jr( R )Hmm is substantially less than unity.

15. A low pass lter for a liquid transmission system of the' type comprising a line anda source of high frequency pulsations for pumping liquid through said line, said lter comprising a liquid filled surge chamber having a pressure communication with the liquid owing in s aid lfne and a choke tube interposed between the surge chamber and line, said surge chamber having, a Volume sucient' to absorb excess flow during pressure peaks and said choke tubev having a length which is small compared to the wave lengths of strong high frequencies which it is desired to lter' and having a cross sectionk which is small compared to the cross section ofthe linebut which is suiciently large to cause only aA small Vpressure drop.

16. The filter of claim 15 wherein said surge chamber is so situated as to be in the path of ow of liquid which is being pumped and to be filled with such liquid as the surge medium.

17` In a liquid transmission system comprising a source of pulsating pressure including at least one strong high frequency, the improvement which comprises a low pass lter which is untuned with regard to any particular frequency but which will effectively moderate all strong high frequencies, said filter comprising a liquid-filled capacitance of volume V and an nductance; said capacitance being so arranged that the liquid medium thereof will be compressed during pressure peaks and will eX- pand during pressure lows and will impart to the liquid ilow in the system a resultant pulsating 110W; the volume V being such in relation to the compressibility of the liquid medium and the excess ow associated with the pressure peak of any strong high frequency that the capacitance will absorb such excess flow; said inductanee being so arranged as to receive said resultant pulsating flow and being of a magnitude such that it will eiectively choke and moderate such ow.

References Cited inthe le of this patent UNITED STATES PATENTS 2,100,404 Mason et al. Nov. 30, 1937 2,185,023 Crane Dec. 26, 1939 2,351,156 Segel June 13, 1944 2,401,570 Koehler June 4, 1946 2,474,512 Bechtold et al. June 28, 1948 

1. IN COMBINATION WITH A LIQUID TRANSMISSION SYSTEM COMPRISING A SOURCE OF PULSATING PRESSURE GIVING RISE TO PERIODS OF PEAK FLOW WHICH OCCUR AT A HIGH FREQUENCY AND WHICH ARE CHARACTERIZED BY A SMALL EXCESS FLOW OF LIQUID OVER MEAN FLOW, A SURGE CHAMBER FILLED WITH A COMPRESSIBLE MEDIUM WHOSE COMPRESSIBILITY IS SMALL COMPARED TO THAT OF A GAS BUT WHOSE VOLUME AND COMPRESSIBILITY ARE SUCH THAT EXCESS PEAK PRESSURES SUFFICE TO COMPRESS SAID MEDIUM BY AN AMOUNT WHICH IS SUBSTANTIAL IN RELATION TO THE VOLUME OF SAID EXCESS FLOW, AND MEANS CONNECTING SAID SURGE CHAMBER WITH SAID SYSTEM WHEREBY SAID MEDIUM IS ALTERNATELY COMPRESSED AND EXPANDED IN RESPONSE TO PRESSURE PEAKS AND PRESSURE LOWS OF SAID PULSATING PRESSURE, RESPECTIVELY, AND WHEREBY THE PULSATING FLOW OF LIQUID IN SAID SYSTEM IS DAMPENED. 